Horn, trumpet, or like acoustic amplifier



Jam 4, 1927.

E. A. GRAHAM HORN, TRUMPET OR LIKE ACOUSTIC AMPLIFIER Filed Oct. 18, 1924 Patented Jan. 4, 1927.

UNITED STATES PATENT OFFICE;

EDWARD ALFRED GRAHAM, OF BROCKLEY, ENGLAND; MARIA GRAHAM AND ALFRED GRAHAM EXECUTORS 0F SAID EDWARD ALFRED GRAHAM, DECEASED.

HORN, TRUMPET, OR LIKE ACOUSTIC AMPLIFIER.

Application filed October 18, 1924, Serial No.744,513, and in Great Britain January 18v 1924,.

This invention relates to a horn trumpet or like acoustic amplifier for use with loud speaking telephonic receivers and other sound producing or reproducing apparatus, and it has for its object to produce an acoustic amplifier of the kind referred to (here inafter referred to a horn) that shall provide the maximum acoustic amplification consistent with the form or development of the horn, and at the some time allow of an ornamental or artistic exterior finish being imparted to the horn.

In acoustic amplifiers applied to apparitus in which sound waves are produced or originated by the vibration of a diaphragm. as in the case of an electro-magnetic telephonic receiver, it is usual to employ a horn of gradually increasing cross sectional area or capacity from the sound chamber con taining the vibratory diaphragm to its outer extremity which generally develops into a bell mouth.

Such horns whether of straight, bent or curved outline and whether made in one or several parts or sections jointed togeth r, are frequently heavily coated and lined with an enamel which imparts an appearance simulating a coarse and cro s grained leatherknown as Levant grain. This enamel, in addition to imparting an artistic effect or finish, sometimes called a crackle or crystalline surface, to the horn. also possesses further advantages inasmuch as, ow ing to its forming a comparatively thick layer and to its irregular finish it conceals blemishes produced in the horn during manufacture thereof whilst owing to its being of a semi-elastic clu'n'acter, it produces a sound deadening effect tend ng to reduce re onance in the thin metal, or other substance of which the horn is made. The lining of a horn with enamel of the kind reterred to (hereinafter called for distinction sound deadening enamel) does however prejudicially afiect the free development of sound waves passing through the portion of the horn of gradually increasing diameter, extending from its inlet end to its junction with the bell mouth end, and consequently the clarity of the resulting sounds,

Now according to the present invention, in order to retain the advantages of the sound deadening enamel. and at the same time avoid its'disadvantages, the portion of the horn of gradually increasing dian'ieter and made of metal or other suitable material, instead of being covered both internally and externally with the sound deadening enamel, has its exterior portion, or part thereof, covered with such enamel whilst its interior portion is covered with a plain enamel having a clean and smooth finish so that a surface free from inequalities and obstructions in the gradually expanding passage of the horn, is obtained that will allow 0f the free development of the sound waves passing therethrough whilst the coating of sound deadening enamel on the outer surface of the horn imparts an artistic and economical finish with a tendency to minimize resonance in the horn.

An acoustic horn generally develops in cross sectional area in a gradual manner from its inlet end to a point where the flaring or hell month end commences and continues more abruptly and it is only necessary to apply to the gradually developing portion of the horn a coating of the enamel having a clean and smooth finish.

By experiment it has been found that a horn lined with enamel adapted to afford a smooth surface and covered externally with a heavier deposit of the sound deadening enamel has an acoustic efiiciency-that is to say volume of reproduced sound and clarity thereof-01. approximately 20% over and. above that of an equivalent horn. treated internally with the said ound rlmuleninnj enamel in the same manner as the exterior which, as before stated, is the usual practiee.

It will be understood that the treatment hereinbefore described constituting the present invention can he applied to sound amplifying horns of any shape whether constructed in one, two or more sections.

In the accompanying drawings, Fig. 1. shows partly in longitudinal section and partly in side elevation and, by way of on only, one con truction at na -a am hod ring the invention, Fig. 2 lin ng a similar view of another constrin-tion ot h rn.

In the example according to Fig. l. the horn made of thin sheet material, tor instance metal, comprises a straight portion 0, of gradually increasing diameter and a liaring or bell mouthed shaped outlet port on (1 the smaller or inlet end ot' the horn being adapted to be connected to a telephone receiver 7) or other sound producing device. lhe inner surface ot' the portion (1 of the horn is lined with a laver ot enamel c p esenting a hard and smooth surface while the outer surface of both portions r: and a of the horn are coated with a laver o't sound deadening enamel Z of the kind hereinhefore referred to. adapted to allord a coarse cross grained, roughened or crackle surface of the kind menti ned. The inner surtace of the hell mouthed portion (1 of the horn may be lined with enamel of the kind used to line the traight portion (4 ol the horn and impart a hard and sn'iooth sur; .ce thereto. but it may, if desired. and {or tie sake of appearance, be lined as shown with sound deadening enamel (Z similar to that applied to the exterior of the horn. as it only particularly essential to provide a mooth unohstructed and non-sound 21l:StHlH-]ltl layer of enamel c to the interior of the longer and gradually tapering portion o (it the horn.

in Fig. 2 the horn comprises a huilt up hell mouth portion c o? non-metallic material tor instance wood. which need not he enamelled in an v wayeither interna -l or externallv, the remaining portion oi. the horn howerer 0t graduall increasing diameter from its inlet end being provided with a smooth lining c and with an exterior covering having a crackle surface (Z as in the previous example.

In each case, the enamels c and (Z are separately applied as layers thereot to the inner and outer surtaces ot the horn and are not naturally present thereon as a glaze or roughened surl'acc.

Vi'hat 1 claim isz 1. For a loud speaking telephonic receiver or other sound producing or re 'n'oducing a pparatus. an acoustic horn-like amplifier comprising a portion of gradually increasing cross sectional area from the end to which a sound producing chamber s to be attached, and a hell mouth of more aluuptl increasing cross sectional area, said first mentioned p rtion having an applied lining of enamel atto ding a hard smooth. surface and an ap ilieil exterior coating of sound deadeni l 7 is cnsnicl affording a coarse cross grained,

roughe i or crackle surface, suliisti'intiall as described.

2. For a loud speaking telephonic receiver or other sound producing or reproducing apparatus, an acoustic horn-like amplifier comprising a portion of gradually increasing cross sectional area 'l'roin the end to which a sound producing chamber to l E attached, and a hell mouth of more abruptly increasing cross sectional area, said first mentioned portion having an applied lining of enamel atlording a hard smooth surface and an ap plied exterior coating of sound deadening enamel atlording a coarse cross grained, roughened or crackle surface, and said. hell month having a :oatinnj ot like sound deadening material, substantially as described.

3. For a loud speaking telephonic receiver or other sound producing or reproducing apparatus, an acoustic horn-like amplifier co1nprising a portion of gradually increasing cross sectional area from the end to which a sound producing chamber is to be attached, and a bell mouth of more abruptly increasing cross sectional area, said first mentioned portion having an applied lining of enamel a'l'i'ording a hard smooth surface. and an up plied exterior coating of sound deadening enamel attording a coarse cross grained, roughened or crackle surface, and said hell mouth having both a coating and lining of like sound deadening material, substantially as described.

-'l-. For a loud speaking telephonic receiver or other sound producing or reproducing apparatus, an acoustic horn-like amplifier com prising a sheet metal portion of gradually increasing cross sectional area "from the end to which a sound producing chamber is to be attached, and a hell mouth of more alnruptlv increasing cross sectional area, said iii-st mentioned portion haring an applied lining of enamel altording a hard smooth surface and an applied exterior coating of sound deadening enamel atljording a coarse cross grained, roughened or crackle surface, substantially as described.

5. For a loud speaking telephonic receiver or other sound producing or reproducing up paratus, an acoustic horn-like amplifier comprising a sheet metal portion of gradually ii'icreasing cross sectional. area l'rom the end to which a sound producing chamber is to he attached. and a sheet metal hell mouth ot more alu'uptl increasing cross sectional area, said first u'icntioncd portion lltlVlllQ' an applied lining oi enamel :il'lhi'diiig' a hard smooth surface and an applied exterior coating of sound deadening enamel al'o. l a coarse cross rained, roughened or e: crackle surface. and said. bell nnnith having a coal ing o't like sound deadening material, substantially as described.

6. For a loud speaking telephonic receiver or other sound producing or reproducing aplmratus, an acoustic horn-like amplifier ;t'ormed of sheet metal and comprising a pon tion of graduallv increasing cross sectional area from the end to which a sound producing chamber is to be attached, and a hell mouth of" more abruptly increasing cross sec tional area, said first mentioned portion having an applied lining of enamel. affording a hard smooth surface and an applied exterior coating of sound deadening enamel aflording a coarse cross grained, roughened 0r crackle surface, and said bell mouth having both a coating and lining of like sound deadening material, substantially as described.

Signed at London, England, this thirteenth day of September, 1924.

EDWARD ALFRED GRAHAM. 

